In recent years, now that environmental pollution and energy saving are coming to be regarded as serious problems, new processes have been developed which bring about the oxidation of organic matter in water via the biological action of microorganisms (e.g., Japanese Tokkai Sho 62-3784, Tokkai Hei 3-127692 and Tokkai Hei 4-222587).
However, despite increasingly serious pollution of the world's lakes and oceans, and the fact that pollution is now affecting even ponds and marshes, no device has yet been developed which provides a solution to the problem.
The inventors, as a result of intensive studies on the purification of polluted water in outdoor locations such as ponds, lakes and marshes, developed a method whereby a treatment tank which floats on the water surface comprising a plurality of biological supports having biological activity extending into the polluted water. Polluted water is efficiently purified without removing it to another location by passing it through the tank. In particular, they found that, when light was shielded from part of the passage through which the polluted water passes, water-bloom dries up and dies so that highly efficient and easy purification can be achieved.